This invention relates to a sheet handling system for dividing a stream of sheets into at least two streams of sheets for at least two delivery stations.
Although the present invention has general application in sheet handling systems, it is particularly applicable in printing presses in which webs are printed and folded into ribbons, and the ribbons are cut into folded sheets or signatures. Normally a number of pages are printed by the printing cylinder so that there are a number of different signatures in the stream emerging from the cutter between repeat signatures. The delivery section of the printing press usually separates like signatures and directs them to different conveyors in stacked or overlapping fashion which serve as collection stations for repeat signatures. The signatures are then usually delivered to an inserter for assembling and stitching them in a book.
The conventional delivery section of a printing press includes a plurality of transfer cylinders utilizing pins or grippers to engage the signatures and direct them along appropriate paths of travel to the proper collection stations. These pins and grippers are controlled by actuating means operated in timed relation with the travel of the leading edges of the signatures to insure proper handling.
For example U.S. Pat. No. 3,032,335 shows a folder in which the cylinders 34 and 35 mount pins which impale and hold the free end of the web, knife assemblies to sever the signatures from the web, and tucker blades and folding jaws for putting a transverse fold in each signature. Alternate ones of the signatures are taken from each of the cylinders 34 and 35 by a distributing cylinder, which also slows the signatures. Each distributing cylinder separates successive signatures into two streams of signatures that are fed to longitudinal folders.
U.S. Pat. No. 3,459,421 is similar in that the product is cut off, impaled on pins and folded before being presented to a gripper and slowdown cylinder which separates successive signatures into two streams that are fed to fan wheels by way of additional gripper and slowdown cylinders.
The use of pins to engage and transfer a signature means that the pin holes must be trimmed out and correspondingly less area of the signature is available for printing. Also, perforated signatures tend to stick to each other causing problems in signature handling. Furthermore, folders having knife assemblies installed on the pin cylinders are limited to a fixed cut off length determined by the cylinder diameter and the number of knife assemblies.
U.S. Pat. No. 4,373,713 shows a signature delivery apparatus in which a stream of sheets or signatures are divided into two streams that are supplied to fan wheels, using a pair of rotary diverter cams cooperating with a pair of stationary guide surfaces, guide tapes conducting the signatures between the diverter cams.
This arrangement is limited in its variable size range capability due to the size which the cams must maintain in order to match the surface speed of the tapes, and the placement of the adjacent tape guide rolls so that the signature is always contained in a tape nip. Another difficulty is that a stationary guide is known to mark a printed surface that strikes it at high speed. Also, this arrangement is limited to a single width folder in order to provide accessability to the tapes under the diverter cams.